aws_ecs_service: availability_zone_rebalancing attribute shouldn't have a default

[nina-nee]

Description

An attributed availability_zone_rebalancing that was introduced in PR #40225 is defined as an optional, but also has a default value. For configurations where this flag is not defined, plan with refresh=false results in a change that would add this attribute to the state - which is not what "optional" should mean.

Relations

Closes #40349

Output from Acceptance Testing

Local tests pass, but I do not have an AWS account I could use for acceptance testing at the moment, sorry.

[github-actions]

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[github-actions]

Welcome @nina-nee 👋

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